Many research institutions are currently conducting research to develop Silicon Carbide (SiC), the SiC has been already supplied as power device products all around the world from a plurality of companies. Advantages of power devices formed using SiC which is a wideband gap semiconductor include lower on-resistance, higher switching speed, higher temperature operation, etc., than conventional Si power devices.
However, when power modules for switching large currents at high frequencies by utilizing such high-speed switching characteristics are fabricated, it causes problems, e.g., an increase of switching power losses or avalanche breakdown of the power devices due to voltage surges, or malfunctions of main transistor due to gate voltage vibration resulting from current inflows to feedback capacitance if parasitic inductances of ringing loops which strongly affect an amount of surge voltages to be applied to the power devices to be built-in are not sufficiently decreased.
There is a method of using laminated wiring for wiring bus (BUS) in modules, as one of the methods for reducing parasitic inductances of power modules. However, when using transfer-mold type power modules, it is difficult to introduce the laminated wiring at a periphery of externally-exposed terminal units in particular due to a relationship of fixing objects to be molded by pressing down terminals with metallic molds etc., in a case of molding, and parasitic inductances of terminals become a stumbling block therefor also in a viewpoint of securing a creepage distance between terminals.
In order to solve such a problem, a circuit unit which can form a semiconductor element at an OFF state and a closed loop having low inductance is formed without including an externally-exposed terminal by disposing an internal capacitor nearer to a side of a bridge than a terminal connection unit, and, thereby the voltage surges can be reduced.